Server computers, as deployed in data centers, can be categorized as either top-loading or front/back loading. FIGS. 1A and 1B illustrate an example of a top-loading server. The server enclosure 100, which has a server compartment 101 and a drive bay 102 is shown pulled out of a rack with the top lids 103a, 103b in an open configuration. As shown, mass storage devices such as hard disk drives (HDDs) or solid state drives (SSDs) 180 are inserted from the top of the server enclosure 100 to mate with connectors on a base board which is functionally connected with some logic. In the case of 3.5″ large form factor (LFF) drives, this design is highly efficient and allows for the densest packing of storage media while maintaining the best possible service model.
A front/back (or rear) loading server enclosure 200 is shown in FIG. 2. As shown, the drives 280 are inserted horizontally into the open front or back end 204 of the server enclosure 200 which makes up the drive bay 202 of the enclosure 200 to mate with a back plane, drive plane or mid plane. The mid plane provides the electrical interface for the drives with a compute node installed in the compute compartment of the enclosure 200. This design allows for fixed mounting of the server in a rack where the drives are simply pulled out or inserted by operating a lever on a drive carrier to cam the drive's connector in and out of the mating connector on the drive plane. The distinction of front vs. rear loading only refers to the drives facing the hot or cold isle, respectively, in a data center.
Front and rear loading server designs have the disadvantage of allowing only a relatively small number of drives as defined by the cross sectional area of the server's face. For example, a 2 U height server in a standard 19″ rack can accommodate twenty four 2.5″ small form factor (SFF) drives or 12 3.5″ LFF drives. Of particular relevance is the use of 2.5″ SFF drives in vertical orientation that fit into the envelope of a 2 U server with 3.5″ outside z-height. A variant of this design is a side loading server 300 shown in FIG. 3, in which both sides can be used to insert drives in to a drive bay 302 extending behind the compute enclosure 301. In a 2 U enclosure, 30 drives 380 per side can be inserted horizontally through an opening 304 into the drive bay 302, however, in a 19″ rack width configuration, this leaves a large center channel of the enclosure as unused space. The drives can be standing on edge as shown or lying flat, depending on the specific design.
Several mechanisms have been developed to utilize this unused space including cantilevered drive planes but all currently available solutions are mechanically overly complicated, problematic with respect to signal integrity and/or expensive to manufacture.
In light of the above it is clear that simpler and more robust solutions are needed that better utilize the existing footprint of servers with SFF drives.